Conventionally, optical transceivers with data rates up to 4 Gb/s are packaged in small form factor (SFF or SFP) packages, while optical transceivers with higher data rates, e.g. 10 Gb/s, are in larger packages, such as XFP, X2, and XENPAK. A conventional XFP arrangement is illustrated in FIG. 1, in which an XFP transceiver module 1 is plugged into a host cage assembly 2 mounted on a host circuit board 3. The host cage assembly 2 includes a front bezel 4, a cage receptacle 5, and a host electrical connector 6. The transceiver module 1 is inserted through an opening in the front bezel 4, and through an open front of the cage receptacle 5, until an electrical connector on the transceiver module 1 engages the host electrical connector 6. The cage receptacle 5 has an opening 7 in the upper wall thereof through which a heat sink 8 extends into contact with the transceiver module 1 for dissipating heat therefrom. A clip 9 is provided for securing the heat sink 8 to the cage receptacle 5 and thereby into contact with the transceiver module 1. With this arrangement, the heat sink 8 can be changed to suit the owner's individual needs without changing the basic transceiver module 1.
Examples of conventional heat sinks are disclosed in U.S. Pat. No. 6,916,122 issued Jul. 12, 2005 in the name of Branch et al.
Pluggable optic module thermal dissipation requirements are increasing with the continued advancement of features and performance. 10 Gb/s modules with added features, e.g. EDC, tenability etc., have increased the power density of pluggable optics, and speed increases to 40 Gb/s and 100 Gb/s are pushing power densities even higher. A fundamental problem for all pluggable (removable) optical modules in telecom systems is that the need to make them removable limits the thermal conduction path. Improvements to the thermal conduction path will reduce the need for faster cooling air speeds or larger heat sinks, which are not always capable of keeping the modules within the operating temperature ranges specified.
The most common approach to connecting a heat sink to a pluggable optical module is the use of the MSA-suggested heat sink 8, which clips to the cage 2 using the spring clip 9. The spring clip 9 enables the heat sink 8 to move slightly, i.e. up and down, side to side, forwards and back, when the pluggable optic module 1 is inserted/extracted, while maintaining a tight interface between the surface of the module 1 and the heat sink 8. However, the surfaces of the heat sink 8 and the pluggable optic module 1 are made of hard, non-conforming metal. This metal-to-metal contact is the weak link in the thermal path. Microscopic imperfections in the heat sink 8 and surfaces on the module 1 limit the flow of heat across the interface. Thermal contact resistance causes large temperature drops at the interfaces, which negatively affect the thermal performance of the system. Thermal management can be significantly better if there are no high resistance interfaces in the system.
In non-sliding applications a thermal interface material, e.g. gel, is often used to improve the thermal interfaces by filling the imperfections and improving heat flow. However, in a sliding application, e.g. pluggable optics modules (SFP, SFP+, GBIC, XFP, XENPAK, XPAK, X2) traditional thermal interface materials are undesirable because the thermal interface for pluggable optics is transient in nature. Modules will be extracted and inserted multiple times. Thermal interface materials leave residue on modules as they are removed, they dry out when no module is present (shipping) and are generally awkward to apply.
An object of the present invention is to overcome the shortcomings of the prior art by providing heat-sinking pluggable optical modules which addresses the need to be able to insert and remove MSA standard or other optical modules. The solution provides greatly improved thermal conductivity between the optical module and the heat sink within the system.